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A first record of a terrestrial mollusc without a radula

1998; Oxford University Press; Volume: 64; Issue: 2 Linguagem: Inglês

10.1093/mollus/64.2.249

1464-3766

Justin Gerlach, A.C. van Bruggen,

Mollusks and Parasites Studies

Recent examination of a series of carnivorous terrestrial gastropods from Seychelles has revealed the absence of the radula and odontophore cartilage in the exceptional species Imperturbatia perelegans (Martens, 1898) (family Streptaxidae). Observations of a captive individual identify the species as at least in part a carrion feeder and the specialisation of feeding structures as adaptations to feeding on softbodied prey. This is the first time that a terrestrial mollusc has been identified as lacking this typically molluscan structure. A large collection of Seychelles carnivorous terrestrial gastropods of the family Streptaxidae was made by Drs. P.G.L. Benoit and J.-J. Van Mol for the Mus6e Royale de 1'Afrique Centrale in 1972 and by the senior author in 1988-96. These collections are being examined as part of a taxonomic revision. Recently completed dissections have identified the endemic genus Imperturbatia as a diverse grouping of highly specialised taxa. One of these, /. perelegans, is represented by numerous shells and by only two spirit-preserved specimens. Dissection of these has revealed the most extreme dietary specialisation detected in the family to date. In all other streptaxids dissected during this study and in publications, the radula and odontophore cartilage are extremely highly developed, being the most muscular structures in the body and occupying at least a third of the body cavity. In /. perelegans all radular structures are completely absent. Neither the radula nor the supporting odontophore are developed. There is also no trace of the associated retractor muscles. The complete absence of these structures is confirmed in both preserved adult specimens available for dissection. This demonstrates that radular absence is a normal feature of the species and not a pathological condition of a single individual.